As discussed in U.S. Pat. Nos. 7,042,108 and 6,563,229, the disclosures of which are incorporated herein by reference, sensitive loads, such as computers, data processing equipment, communications equipment, and the like, require stable and uninterrupted power. Accordingly, many such items include battery backup power supplies. However, battery power is not sufficient for large power grids, such as might be associated with utility power sources. Furthermore, battery failures due to constant charging are a common problem in the standby power generation industry and thus battery backup systems may have problems, including reliability problems.
Therefore, there is a need for a standby and backup power system that does not require batteries.
Synchronous condensers and synchronous motors are used on power systems where large amounts of reactive KVA are needed for power factor correction and voltage regulation. A synchronous condenser is similar to a synchronous motor, but is built to operate without a mechanical load, primarily to supply reactive KVA, which is main component of voltage regulation and stabilization. For example, on a decrease of Line Voltage down to 70% of rated, the leading reactive component of a leading power factor machine will increase maintaining constant voltage to the load to which it is connected. On over voltage, for example up to 10% of rated, the reactive component of a leading power factor machine will decrease maintaining constant voltage to the load to which it is connected. Synchronous condensers, due to their low impedance and ability to generate reactive KVA will protect a load by filtering out transients and maintaining constant voltage during sags and interruptions. However, during longer interruption of utility power, synchronous condensers may be inadequate.
Synchronous machines are also ideal components in dynamic No-Break or Continuous power systems since they can constantly rotate on a line connected to the utility with the load being a condenser or a generator.
Therefore, large systems often utilize rotating continuous electric power generation systems as a source of standby or backup power. Such standby or backup power systems are connected in parallel with utility power. Such systems must constantly monitor voltage, frequency and power shape and should be able to detect irregularities and disconnect instantly from the utility when an indicia of power falls below a preset value or when power is interrupted.
When a synchronous condenser is coupled to a mechanical load for use in a continuous or no-break power system, during voltage sags or interruptions, the mechanical load will instantly turn the condenser into a generator. This will change the Vector and the Power Factor of the machine. Therefore, instead of generating the leading reactive current necessary for voltage regulation, it begins to generate KW. Once the condenser turns into a generator, the re-connect of the utility out of phase becomes a critical issue.
Power failure detection and isolation from utility source in time is a critical function for any rotating continuous power system since the synchronous machine (motor) instantly turns into a generator when electric drive power to it is interrupted. If a utility breaker is not immediately opened, the generator will back feed the entire grid and may also fail due to overload.
Therefore, rotating power protection systems use a variety of means to provide such immediate interruption. For example, some systems use computers and other digital equipment to monitor the power quality and send and receive signals to and from remote locations. The power to drive these devices usually comes from the generator. However, once the generator is connected in parallel to the utility, any disturbance on the utility line, such as lightning strikes or the like, may have direct consequences on these very same monitoring and protection devices. In some cases, these devices may fail to detect a power interruption in time or fail completely due to problems associated with their configurations and connections to the system. Such failure will render the entire power protection system useless.
In order to overcome some of the problems discussed above, some systems include a taped series reactor between the utility, the generator and the load. These systems are sometimes called “isolating couplings” or “line-interactive filters.” With this configuration, voltage between the line and the tap is monitored as well as between the generator and the tap. The reactor will always provide a preset power factor and generate reactive power in both the line and the load direction in order to minimize possible damage during momentary interruptions as well as to provide reactive power for load regulation.
There are several problems with this solution. The inductor changes the load impedance during both normal and/or during emergency power generation and limits the short circuit clearing ability of the system or necessary current required for motor starting and other inductive type equipment thereby limiting its applications.
A-C frequency sensing switches are also used for power failure sensing. When power to a synchronous motor is interrupted, the rotating field of the machine begins to slow thereby generating lower frequency. Normally, these devices are set to disconnect the load and the machine from the utility at 59.9 Hz in a 60 Hz system. This only allows 0.5 Hz frequency deviations. However, during peak load conditions, it is quite common to have utility frequency variations of 0.5 Hz. Therefore, using any type of frequency or shift speed sensing device as a primary and only sensing method can be unreliable.
A solution is described in U.S. Pat. No. 5,684,348 which discloses a rotating field of a synchronous machine or coupling with a built in mechanical switch. The mechanical switch is allowed 90° electrical slip so that at the end of the slip, the switch can send a signal to isolate the machine from a faulty circuit. However, there are several problems with this approach. First, it may be difficult and costly to integrate a mechanical switch into a rotating Field of a generator or even a coupling and be able to send a contact signal. Furthermore, the described 90° electrical slip represents 0.5 Hz frequency loss even before the breaker open signal can be generated. Furthermore, the possibility of a utility re-connect at 90° out of phase may damage and may even destroy the coupling of the switch, or may even bend the shaft of the machine as well as create large transients.
Therefore, the amount of slack within the coupling should be minimized to maintain closer frequency regulation but long enough to provide the transitional KVA until the system is isolated from the faulty source.
Therefore, there is a need for a power system that is equipped with a positive failsafe system for monitoring and power failure sensing along with a reliable source of energy to start a standby machine.
More specifically, there is a need for a power system that is equipped with a positive failsafe system for monitoring and power failure sensing along with a reliable source of energy to start a standby thermal engine.
While the systems disclosed in the incorporated patents, U.S. Pat. Nos. 6,653,229 and 7,042,108 provide excellent solutions to the above-discussed problems, there is room for improvement in this field. In some situations, a mechanical means for detecting slip between a main power source and a flywheel is more reliable than an electronic means.